1. Field of the Invention
This invention relates to a metal wiring on a semiconductor element, and related method. In particular, the present invention uses an aluminum film to prevent oxygen from being diffused into copper contained in the metal wiring.
2. Description of the Related Art
In ULSI (Ultra Large Scale Integrated Circuit) class semiconductor elements, copper (Cu) is used for the metal wiring layer. Copper has a lower resistivity than aluminum and excellent electro-migration characteristics. However, since copper is susceptible to oxidation, a metal wiring formed of copper should be covered with a protective layer to prevent oxidation.
FIG. 1 is a sectional view of a conventional semiconductor element having a copper metal wiring layer. Briefly, a copper metal wiring layer 2 having an exposed surface is formed on a designated part of a semiconductor substrate 1. An oxidation prevention film 3 is then formed on the exposed surface of the copper metal wiring layer 2 for inhibiting diffusion of oxygen into the copper.
A method for forming the structure shown in FIG. 1 will now be discussed in greater detail.
First, a copper film is deposited on an exposed surface of the semiconductor substrate 1. Then, the deposited copper film is patterned around a pattern mask using a photoetching process to form the copper metal wiring layer 2. An oxidation prevention insulation film is then deposited on the entire exposed surface of the substrate to a thickness of about 500.ANG.. The deposited oxidation prevention insulation film is selectively removed around a pattern mask using a photoetching process to form the oxidation prevention film 3.
The oxidation prevention film 3 prevents oxygen from being diffused into the copper metal wiring layer 2 during a heat treatment in an atmosphere such as in an oxygen atmosphere. The oxidation prevention film includes, for example, TiN, TiW, TiWN, TaN, NbN, or a single metal layer of Ti, Cr or W. In general, however, the oxidation prevention film is composed of a stable chemical with a low mutual solid solubility, a low mutual diffusing speed, and a material that inhibits the diffusion of oxygen for the oxidation prevention film. As a result, as shown in FIG. 2, which illustrates the distribution of oxygen density at each layer of the semiconductor element shown in FIG. 1, even though the semiconductor is subjected to a heat treatment in an atmosphere such as oxygen, the oxidation prevention film prevents oxygen from being diffused into the metal wiring layer 2.
The conventional semiconductor element has the following problems.
First, the conventional method for fabricating the metal wiring is complicated because, it is necessary to both deposit and pattern the copper and the oxidation prevention material, requiring several mask steps.
Second, element integration is reduced due to the increased line width of the metal wiring layer. Further, since the oxidation prevention film has a thickness of about 500.ANG., the resistance of the metal wiring is significantly increased, thereby deteriorating electrical characteristics of the wiring layer.